Simplified method to produce nanoporous silicon-based films

ABSTRACT

An improved nanoporous dielectric film useful for the production of semiconductor devices, integrated circuits and the like, is provided, together with novel processes for producing these improved films. The improved films are produced by a process that includes  
     (a) preparing a silicon-based, precursor composition including a porogen,  
     (b) coating a substrate with the silicon-based precursor to form a film,  
     (c) aging or condensing the film in the presence of water,  
     (d) heating the gelled film at a temperature and for a duration effective to remove substantially all of said porogen, and  
     wherein the applied precursor composition is substantially aged or condensed in the presence of water in liquid or vapor form, without the application of external heat or exposure to external catalyst.

FIELD OF THE INVENTION

[0001] The present invention relates to novel nanoporous silicadielectric films having improved mechanical strength, and tosemiconductor devices comprising these improved films. The presentinvention also provides improved processes for producing the same onsubstrates suitable for use in the production of semiconductor devices,such as integrated circuits. The nanoporous films of the invention areprepared using silicon-based starting materials and polymers,copolymers, oligomers, and/or compounds, and are prepared by asimplified process that, in one embodiment, allows for aging or gelationwithout heating.

BACKGROUND OF THE INVENTION

[0002] As feature sizes in integrated circuits approach 0.25 μm andbelow, problems with interconnect RC delay, power consumption and signalcross-talk have become increasingly difficult to resolve. It is believedthat the integration of low dielectric constant materials for interleveldielectric (ILD) and intermetal dielectric (IMD) applications will helpto solve these problems. While there have been previous efforts to applylow dielectric constant materials to integrated circuits, there remainsa longstanding need in the art for further improvements in processingmethods and in the optimization of both the dielectric and mechanicalproperties of such materials used in the manufacture of integratedcircuits.

[0003] Nanoporous Films

[0004] One material with a low dielectric constant are nanoporous filmsprepared from silica, i.e., silicon-based materials. Air has adielectric constant of 1, and when air is introduced into a suitablesilica material having a nanometer-scale pore structure, such films canbe prepared with relatively low dielectric constants (“k”). Nanoporoussilica materials are attractive because similar precursors, includingorganic-substituted silanes, e.g., tetraethoxysilane (“TEOS”), are usedfor the currently employed spin-on-glasses (“S.O.G.”) and chemical vapordeposition (“CVD”) of silica SiO₂. Nanoporous silica materials are alsoattractive because it is possible to control the pore size, and hencethe density, mechanical strength and dielectric constant of theresulting film material. In addition to a low k, nanoporous films offerother advantages including: 1) thermal stability to 900° C., 2)substantially small pore size, i.e., at least an order of magnitudesmaller in scale than the microelectronic features of the integratedcircuit, 3) as noted above, preparation from materials such as silicaand TEOS that are widely used in semiconductors, 4) the ability to“tune” the dielectric constant of nanoporous silica over a wide range,and 5) deposition of a nanoporous film can be achieved using toolssimilar to those employed for conventional S.O.G. processing.

[0005] Thus, high porosity in silica materials leads to a lowerdielectric constant than would otherwise be available from the samematerials in nonporous form. An additional advantage, is that additionalcompositions and processes may be employed to produce nanoporous filmswhile varying the relative density of the material. Other materialsrequirements include the need to have all pores substantially smallerthan circuit feature sizes, the need to manage the strength decreaseassociated with porosity, and the role of surface chemistry ondielectric constant and environmental stability.

[0006] Density (or the inverse, porosity) is the key parameter ofnanoporous films that controls the dielectric constant of the material,and this property is readily varied over a continuous spectrum from theextremes of an air gap at a porosity of 100% to a dense silica with aporosity of 0%. As density increases, dielectric constant and mechanicalstrength increase but the degree of porosity decreases, and vice versa.This suggests that the density range of nanoporous films must beoptimally balanced between the desired range of low dielectric constantand the mechanical properties acceptable for the desired application.

[0007] Nanoporous silica films have previously been fabricated by anumber of methods. For example, nanoporous films have been preparedusing a mixture of a solvent and a silica precursor, which is depositedon a substrate suitable for the purpose. Broadly, a precursor in theform of, e.g., a spin-on-glass composition is applied to a substrate,and then polymerized in such a way as to form a dielectric filmcomprising nanometer-scale voids.

[0008] When forming such nanoporous films, e.g., by spin-coating, thefilm coating is typically catalyzed with an acid or base catalyst andwater to cause polymerization/gelation (“aging”) during an initialheating step.

[0009] More recently, U.S. Pat. No. 5,895,263 describes forming ananoporous silica dielectric film on a substrate, e.g., a wafer, byapplying a composition comprising decomposable polymer and organicpolysilica i.e., including condensed or polymerized silicon polymer,heating the composition to further condense the polysilica, anddecomposing the decomposable polymer to form a porous dielectric layer.This process, like many of the previously employed methods of formingnanoporous films on semiconductors, has the disadvantage of requiringheating for both the aging or condensing process, and for the removal ofa polymer to form the nanoporous film. Furthermore, there is adisadvantage that organic polysilica, contained in a precursor solution,tends to increase in molecular weight after the solution is prepared;consequently, the viscosity of such precursor solutions increases duringstorage, and the thickness of films made from stored solutions willincrease as the age of the solution increases. The instability oforganic polysilica thus requires short shelf life, cold storage, andfine tuning of the coating parameters to achieve consistent filmproperties in a microelectronics/integrated circuit manufacturingprocess.

[0010] As mentioned supra, there is a continuing need in themicroelectronics industry to provide improved materials allowing forsemiconductor devices, such as integrated circuits, with increasedcircuit density, and increased processing speed and power. This iscoupled with a continuing desire to reduce the cost in time, money andmanufacturing equipment of producing such semiconductor devices. Thus,there remains this ongoing need for further improvements in both thedesirable properties of nanoporous dielectric films, as well as anongoing need for further improvements in methods for producing suchnanoporous dielectric films.

SUMMARY OF THE INVENTION

[0011] In order to solve the above mentioned problems and to provideother improvements, the invention provides novel nanoporous silicadielectric films with a low dielectric constant (“k”), e.g., typicallyranging from about 1.5 to about 3.8, as well as novel new methods ofproducing these dielectrics films.

[0012] Broadly, the dielectric nanoporous films of the invention areprepared by a method that includes the following process steps:

[0013] (a) preparing a silicon-based, precursor composition including aporogen,

[0014] (b) coating a substrate with the silicon-based precursor to forma film,

[0015] (c) aging or condensing the film in the presence of water,

[0016] (d) heating the gelled film at a temperature and for a durationeffective to remove substantially all of the porogen.

[0017] Advantageously, in the above-described process steps, theprecursor composition is substantially aged or condensed in the presenceof water in liquid or vapor form, without the application of externalheat or exposure to external catalyst.

[0018] The artisan will appreciate that the molar ratio of water to Sican be readily determined by the desired rate of condensation and thesuccessful production of nanoporous silica dielectric films. Inparticular embodiments, the molar ratio of water to Si ranges, e.g.,from about 2:1 to about 0:1.

[0019] Broadly, the silicon-based precursor composition includes amonomer or prepolymer according to Formula I:

Rx—Si—Ly  (Formula I)

[0020] wherein x is an integer ranging from 0 to about 2, and y is aninteger ranging from about 2 to about 4;

[0021] R is independently selected from the group consisting of alkyl,aryl, hydrogen and combinations thereof;

[0022] L is an electronegative moiety, such as, e.g., alkoxy, carboxy,amino, amido, halide, isocyanato and combinations thereof.

[0023] The silicon-based precursor composition optionally includes oneor more monomers or prepolymers of Formula I, as well as a polymerformed from the condensation of one or more different monomers orprepolymers according to Formula I. The polymer formed from Formula Ihas a molecular weight, for example, that ranges from about 150 to about10,000 amu.

[0024] Useful monomers or prepolymers include, e.g., acetoxysilane, anethoxysilane, a methoxysilane, and combinations thereof. Particularmonomers or prepolymers useful according to the invention also include,e.g., tetraacetoxysilane, a C₁ to about C₆ alkyl oraryl-triacetoxysilane, and combinations thereof. The triacetoxysilaneis, for example, a methyltriacetoxysilane. Further monomers orprepolymers useful according to the invention also include, e.g.,tetrakis(2,2,2-trifluoroethoxy)silane, tetrakis(trifluoroacetoxy)silane,tetraisocyanatosilane, tris(2,2,2-trifluoroethoxy)methylsilane,tris(trifluoroacetoxy)methylsilane, methyltriisocyanatosilane andcombinations thereof.

[0025] Optionally, the water employed for the processes of the inventionis added to the silicon-based, precursor composition prior to theapplication of the precursor composition to the substrate. Variations onthis process include the addition of amounts of water to thesilicon-based, precursor composition insufficient to fully condense orage the applied film, and completing the aging process by exposing theapplied film to environmental water vapor. In one particularlyconvenient embodiment of the invention, no water is added to thesilicon-based, precursor composition prior to application to thesubstrate. Instead, all of the water for aging the film is provided byenvironmental, e.g., atmospheric water vapor present in the controlledatmosphere of the processing facility. The atmospheric partial pressureof water vapor in the processing facility can be adjusted to range, forexample, from about 5 mm Hg to about 20 mm Hg, The time required forachieving water-mediated aging depends on the materials selected, on thesource of the water, e.g., mixed into the precursor or fromenvironmental water vapor, and the desired degree of aging. The timeperiod ranges, for example, from about 20 seconds to about 5 minutes, ormore.

[0026] A useful porogen according to the invention is added to theprecursor in an amount ranging from about 2 to about 20 weight percent.The porogen also has a boiling point, sublimation point or decompositiontemperature ranging, e.g., from about 175° C. to about 450° C. Theporogen also has a molecular weight ranging, e.g., from about 100 toabout 10,000 amu, or more particularly, from about 100 to about 3,000amu. In addition, the porogen is selected to be readily removed from theapplied and aged film, e.g., by heating at a temperature ranging fromabout 175° C. to about 300° C., for a time period ranging from about 30seconds to about 5 minutes to remove substantially all of the porogen.

[0027] A solvent is also optionally provided to reduce precursorviscosity and aid film spreading, as required. When a solvent ispresent, the silicon-based, precursor composition includes a solvent ormixture of solvents in an amount ranging, for example, from about 10% toabout 90% by weight. The solvent has a boiling point ranging, forinstance, from about 50 to about 175° C. and is selected, for example,from hydrocarbons, esters, ethers, ketones, alcohols, amides andcombinations thereof. However, to avoid undesirable interactions, thesolvent is not an alcohol when the silicon based monomer or precursorcomprises an acetoxy-functional group. To avoid cross-linkage of thesolvent to the precursor, it should be noted that the solvent optionallydoes not include hydroxyl or amino groups. Nanoporous dielectric filmsprepared by the methods of the invention, as well as semiconductordevices and/or integrated circuits manufactured with such films, arealso provided.

BRIEF DESCRIPTION OF THE FIGURE

[0028]FIG. 1 Illustrates the pore volume distribution (Y-axis) plattedagainst the log of the pore size (X-axis).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] Accordingly, nanoporous silica dielectric films having adielectric constant, or k value, ranging from about 1.5 to about 3.8,can be produced by the methods of the invention. Typically,silicon-based dielectric films, including nanoporous silica dielectricfilms, are prepared from a suitable silicon-based dielectric precursorcomposition, e.g., a spin-on-glass (“S.O.G.”) material blended with oneor more optional solvents and/or other components. The dielectricprecursor composition is applied to a substrate suitable, e.g., forproduction of a semiconductor device, such as an integrated circuit(“IC”), by any art-known method.

[0030] The films produced by the processes of the invention have anumber of advantages over those previously known to the art, includingimproved mechanical strength, that enables the produced film towithstand the further processing steps required to prepare asemiconductor device on the treated substrate, and a low and stabledielectric constant. The property of a stable dielectric constant isadvantageously achieved without the need for further surfacemodification steps to render the film surface hydrophobic, as wasformerly required by a number of processes for forming nanoporous silicadielectric films. Instead, the silica dielectric films as produced bythe processes of the invention are sufficiently hydrophobic as initiallyformed.

[0031] Further, in one embodiment, the processes of the inventionadvantageously require no heating step or steps for the initialpolymerization (i.e., gelling or aging) of an applied precursorcomposition onto a substrate. Instead, the precursor composition isselected to be water-polymerizable, and water is either blended with theprecursor prior to application to the desired substrate, and/or afterapplication to a substrate, atmospheric moisture facilitates the agingprocess, in situ. Further still, the processes of the invention providedfor a nanometer scale (10 nm or less) diameter pore size, which is alsouniform in size distribution.

[0032] In order to better appreciate the scope of the invention, itshould be understood that unless the “SiO₂” functional group isspecifically mentioned when the term “silica” is employed, the term“silica” as used herein, for example, with reference to nanoporousdielectric films, is intended to refer to dielectric films prepared bythe inventive methods from an organic or inorganic glass base material,e.g., any suitable silicon-based material. It should also be understoodthat the use of singular terms herein is not intended to be so limited,but, where appropriate, also encompasses the plural, e.g., exemplaryprocesses of the invention may be described as applying to and producinga “film” but it is intended that multiple films can be produced by thedescribed, exemplified and claimed processes, as desired.

[0033] Additionally, the term “aging” refers to gelling, condensing, orpolymerization, of the combined silica-based precursor composition onthe substrate after deposition, induced, e.g., by exposure to waterand/or an acid or base catalyst. The term “curing” refers to the removalof residual silanol (Si—OH) groups, removal of residual water, and theprocess of making the film more stable during subsequent processes ofthe microelectronic manufacturing process. The curing process isperformed after gelling, typically by the application of heat, althoughany other art-known form of curing may be employed, e.g., by theapplication of energy in the form of an electron beam, ultravioletradiation, and the like. The terms, “agent” or “agents” herein should beconsidered to be synonymous with the terms, “reagent” or “reagents,”unless otherwise indicated.

[0034] Dielectric films, e.g., interlevel dielectric coatings, areprepared from suitable precursors applied to a substrate. Art-knownmethods for applying the dielectric precursor composition, include, butare not limited to, spin-coating, dip coating, brushing, rolling,spraying, and/or by chemical vapor deposition. Prior to application ofthe base materials to form the dielectric film, the substrate surface isoptionally prepared for coating by standard, art-known cleaning methods.The coating is then processed to achieve the desired type andconsistency of dielectric coating, wherein the processing steps areselected to be appropriate for the selected precursor and the desiredfinal product. Further details of the inventive methods and compositionsare provided below.

[0035] Substrates

[0036] Broadly speaking, a “substrate” as described herein includes anysuitable composition formed before a nanoporous silica film of theinvention is applied to and/or formed on that composition. For example,a substrate is typically a silicon wafer suitable for producing anintegrated circuit, and the base material from which the nanoporoussilica film is formed is applied onto the substrate by conventionalmethods, e.g., including, but not limited to, the art-known methods ofspin-coating, dip coating, brushing, rolling, and/or spraying. Prior toapplication of the base materials to form the nanoporous silica film,the substrate surface is optionally prepared for coating by standard,art-known cleaning methods.

[0037] Suitable substrates for the present invention non-exclusivelyinclude semiconductor materials such as gallium arsenide (“GaAs”),silicon and compositions containing silicon such as crystalline silicon,polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide(“SiO₂”) and mixtures thereof. On the surface of the substrate is anoptional pattern of raised lines, such as metal, oxide, nitride oroxynitride lines which are formed by well known lithographic techniques.Suitable materials for the lines include silica, silicon nitride,titanium nitride, tantalum nitride, aluminum, aluminum alloys, copper,copper alloys, tantalum, tungsten and silicon oxynitride. These linesform the conductors or insulators of an integrated circuit. Such aretypically closely separated from one another at distances of about 20micrometers or less, preferably 1 micrometer or less, and morepreferably from about 0.05 to about 1 micrometer. Other optionalfeatures of the surface of a suitable substrate include an oxide layer,such as an oxide layer formed by heating a silicon wafer in air, or morepreferably, an SiO₂ oxide layer formed by chemical vapor deposition ofsuch art-recognized materials as, e.g., plasma enhancedtetraethoxysilane oxide (“PETEOS”), plasma enhanced silane oxide (“PEsilane”) and combinations thereof, as well as one or more previouslyformed nanoporous silica dielectric films.

[0038] The nanoporous silica film of the invention can be applied so asto cover and/or lie between such optional electronic surface features,e.g., circuit elements and/or conduction pathways that may have beenpreviously formed features of the substrate.

[0039] Such optional substrate features can also be applied above thenanoporous silica film of the invention in at least one additionallayer, so that the low dielectric film serves to insulate one or more,or a plurality of electrically and/or electronically functional layersof the resulting integrated circuit. Thus, a substrate according to theinvention optionally includes a silicon material that is formed over oradjacent to a nanoporous silica film of the invention, during themanufacture of a multilayer and/or multicomponent integrated circuit.

[0040] In a further option, a substrate bearing a nanoporous silica filmor films according to the invention can be further covered with any artknown non-porous insulation layer, e.g., a glass cap layer.

[0041] Water Condensable Precursor Compositions

[0042] Broadly, the precursor composition employed for formingsilica-dielectric films according to the invention includes one or moresilicon-based monomers and/or polymers that are readily condensed in thepresence of water. The water can be optionally supplied duringpreparation of the liquid precursor composition, absorbed fromenvironmental water vapor, and/or combinations of these.

[0043] For a silicon based monomer or pre-polymer to be reactive withwater, the monomer or prepolymer must have at least two reactive groupsthat can be hydrolyzed. Such reactive groups include, e.g., alkoxy (RO),acetoxy (AcO), etc. Without meaning to be bound by any theory orhypothesis as to how the methods and compositions of the invention areachieved, it is believed that water hydrolyzes the reactive groups onthe silicon monomers to form Si—OH groups (silanols). The latter willundergo condensation reactions with other silanols or with otherreactive groups, as illustrated by the following formulas:

[0044] Si—OH+HO—Si→Si—O—Si+H₂O

[0045] Si—OH+RO—Si→Si—O—Si+ROH

[0046] Si—OH+AcO—Si→Si—O—Si+AcOH

[0047] R=alkyl or aryl

[0048] Ac=acyl (CH₃CO)

[0049] These condensation reactions lead to formation of silicon basedpolymers. Generally speaking, an acid or base is used to catalyze boththe hydrolysis and the condensation reactions. It should be mentionedthat when adding volatile acid or base catalysts to the precursorcomposition there is the potential that some or all of the catalyst willevaporate during deposition of the precursor onto the substrate. Whilesuch evaporative losses can be controlled or compensated for, certainembodiments of the present invention advantageously avoid thisdifficulty by forming an acid catalyst in situ by reaction with water.In particular, the reaction of water with acetoxy groups produces aceticacid; the latter compound is a catalyst for hydrolysis and condensationreactions. Therefore, when using acetoxy and other precursors of thistype, it is not necessary to add catalyst to the precursor composition;

[0050] Thus, in one embodiment of the invention, the dielectricprecursor composition includes a compound, or any combination ofcompounds, denoted by Formula I:

Rx—Si—Ly  (Formula I)

[0051] wherein x is an integer ranging from 0 to about 2 and y is aninteger ranging from about 2 to about 4),

[0052] R is independently alkyl, aryl, hydrogen and/or combinations ofthese,

[0053] L is independently selected and is an electronegative group,e.g., alkoxy, carboxy, halide, isocyanato and/or combinations of these.

[0054] Particularly useful monomers or precursors are those provided byFormula I when x ranges from about 0 to about 2, y ranges from about 2to about 4, R is alkyl or aryl or H, and L is an electronegative group,and wherein the rate of hydrolysis of the Si—L bond is greater than therate of hydrolysis of the Si—OCH₂CH₃ bond. Thus, for the followingreactions designated as (a) and (b):

[0055] a) Si—L+H₂O→Si—OH+HL

[0056] b) Si—OCH₂CH₃+H₂O→Si—OH+HOCH₂CH₃

[0057] The rate of (a) is greater than rate of (b).

[0058] Examples of suitable compounds according to Formula I include,but are not limited to: Si(OCH2CF₃)₄tetrakis(2,2,2-trifluoroethoxy)silane, Si(OCOCF₃)₄tetrakis(trifluoroacetoxy)silane*, Si(OCN)₄ tetraisocyanatosilane,CH₃Si(OCH2CF₃)₃ tris(2,2,2-trifluoroethoxy)methylsilane, CH₃Si(OCOCF₃)₃tris(trifluoroacetoxy)methylsilane*, CH₃Si(OCN)₃methyltriisocyanatosilane,

[0059] In another embodiment of the invention, the dielectric precursorcomposition includes a polymer synthesized from compounds denoted byFormula I by way of hydrolysis and condensation reactions, wherein thenumber average molecular weight ranges from about 150 to about 10,000amu.

[0060] In a further embodiment of the invention, silicon-baseddielectric precursors useful according to the invention includeorganosilanes, including, for example, alkoxysilanes according toFormula II, as taught, e.g., by co-owned U.S. Ser. No. 09/054,262, filedon Apr. 3, 1998, the disclosure of which is incorporated by referenceherein in its entirety.

[0061] Optionally, Formula II is an alkoxysilane wherein at least 2 ofthe R groups are independently C₁ to C₄ alkoxy groups, and the balance,if any, are independently selected from the group consisting ofhydrogen, alkyl, phenyl, halogen, substituted phenyl. For purposes ofthis invention, the term alkoxy includes any other organic group whichcan be readily cleaved from silicon at temperatures near roomtemperature by hydrolysis. R groups can be ethylene glycoxy or propyleneglycoxy or the like, but preferably all four R groups are methoxy,ethoxy, propoxy or butoxy. The most preferred alkoxysilanesnonexclusively include tetraethoxysilane (TEOS) and tetramethoxysilane.

[0062] In a further option, for instance, especially when the precursoris applied to the substrate by chemical vapor deposition, e.g., astaught by co-owned patent application Ser. No. 09/111,083, filed on Jul.7, 1998, and incorporated by reference herein in its entirety, theprecursor can also be an alkylalkoxysilane as described by Formula II,but instead, at least 2 of the R groups are independently C₁ to C₄alkylalkoxy groups wherein the alkyl moiety is C₁ to C₄ alkyl and thealkoxy moiety is C₁ to C₆ alkoxy, or ether-alkoxy groups; and thebalance, if any, are independently selected from the group consisting ofhydrogen, alkyl, phenyl, halogen, substituted phenyl. In one preferredembodiment each R is methoxy, ethoxy or propoxy. In another preferredembodiment at least two R groups are alkylalkoxy groups wherein thealkyl moiety is C₁ to C₄ alkyl and the alkoxy moiety is C₁ to C₆ alkoxy.In yet another preferred embodiment for a vapor phase precursor, atleast two R groups are ether-alkoxy groups of the formula (C₁ to C₆alkoxy)_(n) wherein n is 2 to 6.

[0063] Application Ser. No. 09/111,083, mentioned above, also teachesthat preferred silica precursors for chemical vapor deposition include,for example, any or a combination of alkoxysilanes such astetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane,tetra(methoxyethoxy)silane, tetra(methoxyethoxyethoxy)silane which havefour groups which may be hydrolyzed and than condensed to producesilica, alkylalkoxysilanes such as methyltriethoxysilane silane,arylalkoxysilanes such as phenyltriethoxysilane and precursors such astriethoxysilane which yield SiH functionality to the film.Tetrakis(methoxyethoxyethoxy)silane, tetrakis(ethoxyethoxy)silane,tetrakis(butoxyethoxyethoxy)silane, tetrakis(2-ethylthoxy)silane,tetrakis(methoxyethoxy)silane, and tetrakis(methoxypropoxy)silane areparticularly useful for the invention.

[0064] In a still further embodiment of the invention, the alkoxysilanecompounds described above may be replaced, in whole or in part, bycompounds with acetoxy and/or halogen-based leaving groups. For example,the precursor compound may be an acetoxy (CH₃—CO—O—) such as anacetoxy-silane compound and/or a halogenated compound, e.g., ahalogenated silane compound and/or combinations thereof. For thehalogenated precursors the halogen is, e.g., Cl, Br, I and in certainaspects, will optionally include F. Preferred acetoxy-derived monomersor precursors include, e.g., tetraacetoxysilane, methyltriacetoxysilaneand/or combinations thereof.

[0065] In one particular embodiment of the invention, the silicon-basedprecursor composition includes a monomer or polymer precursor such, forexample, acetoxysilane, an ethoxysilane, methoxysilane and/orcombinations thereof.

[0066] In a more particular embodiment of the invention, thesilicon-based precursor composition includes a tetraacetoxysilane, a C₁to about C₆ alkyl or aryl-triacetoxysilane and combinations thereof. Inparticular, as exemplified below, the triacetoxysilane is amethyltriacetoxysilane.

[0067] Processes for Forming Water Condensed Nanoporous Dielectric Films

[0068] Broadly, in one embodiment of the invention the method of theinvention is conducted by preparing a silicon-based precursorcomposition that includes a porogen that is selected to age or condensein the presence of water, without the application of an external sourceof heat. A desired substrate is coated with the silicon-based precursorby any standard, art-known method, to form a film. The applied film isthen aged or condensed in the presence of water, without the applicationof any external heat. The aged film is then heated at a temperature andfor a duration effective to remove substantially all of the porogen, toprovide a silica dielectric film having a nanometer scale porestructure, with the desired low range of dielectric constant.

[0069] In the absence of water these reactions will not occur. Theprecursor compositions of this invention will be very stable over time,until water is added, because polymer growth will not occur. Whilecertain embodiments of the invention use a precursor comprising water,in many production situations it is preferred that the precursor beprepared without water to avoid the aging and thickening of theprecursor between the time of mixing and the time of application to asubstrate. A thicker, more viscous precursor results in thicker appliedfilms. To avoid this potential problem, one option is to add the waterto the precursor formulation just prior to application to the substrate.Avoiding the potential problems of precursor viscosity increasing overtime is a very important benefit of having the precursor aged orcondensed by environmental water vapor after coating, e.g., during themanufacture of semiconductor devices.

[0070] In overview, the precursor is deposited on the substrate at roomtemperature (15-25° C.), usually by spin coating. Once the precursorcomposition is deposited onto the substrate, the resulting firm willabsorb water from the environment (typically chip manufacturing cleanrooms have relative humidity >30%, typically about 40%). This watervapor is sufficient to age the film in situ. Optionally, the film may beheated at 25-200° C. to hasten the solidification of the film.

[0071] Once the film has aged, i.e., once it is sufficiently condensedto be solid or substantially solid, the porogen can be removed. Thelatter should be sufficiently non-volatile so that it does not evaporatefrom the film before the film solidifies. Generally, the porogen isremoved by heating the film at or above 200° C.

[0072] The precursor composition preferably contains an acid catalyst,either volatile or nonvolatile, depending on processing requirements.Acid catalysts include, e.g., organic acids, such as glacial aceticacid; and inorganic acids such as nitric acid and hydrogen chloride;this catalyst will accelerate the hydrolysis and condensation reactions.A base catalyst (such as amine compounds) may also be added to theprecursor composition for this purpose. Of particular value is thein-situ generation of catalyst by reaction of water with the monomer orpolymer contained in the precursor composition. For example, reaction ofwater with tetraacetoxysilane produces acetic acid.

[0073] A film is judged to be porous if its refractive index (n) is lessthan 1.44. A non-porous film made from the liquid precursor of thisinvention will have a refractive index of 1.44. Air has a refractiveindex of 1.0. The porosity of a film is the % of its volume that is air.The porosity of a film is inversely proportional to n-1. For example, afilm with n=1.27 will haveporosity=100*[(1.44-1)−(1.27-1)]/(1.44-1)=39%.

[0074] Selection of a Porogen or Porogens

[0075] A porogen may be a compound or oligomer or polymer and isselected so that, when it is removed, e.g., by the application of heat,a silica dielectric film is produced that has a nanometer scale porousstructure. The scale of the pores produced by porogen removal isproportional to the effective steric diameters of the selected porogencomponent (as noted supra, the use of a singular term encompasses theplural as well). The need for any particular pore size range (i.e.,diameter) is defined by the scale of the semiconductor device in whichthe film is employed. Thus, for microelectronic applications in whichthe minimum feature size is less than 100 nm, a pore size of 10 nm orless is required. Furthermore, the porogen should not be so small as toresult in the collapse of the produced pores, e.g., by capillary actionwithin such a small diameter structure, resulting in the formation of anon-porous (dense) film. Further still, there should be minimalvariation in diameters of all pores in the pore population of a givenfilm.

[0076] Given the above, it is preferred that porogen is a compound thathas a substantially homogeneous molecular weight and moleculardimension, and not a statistical distribution or range of molecularweights, and/or molecular dimensions, in a given sample. The avoidanceof any significant variance in the molecular weight distribution allowsfor a substantially uniform distribution of pore diameters in the filmtreated by the invetive processes. If the produced film has a widedistribution of pore sizes, the likelihood is increased of forming oneor more large pores, i.e., bubbles, on a dimensional scale of 10 nm orgreater, that could interfere with the production of reliablesemiconductor devices having a minimum feature size of less than 100 nm,

[0077] Preferrably, the porogen has reactive groups, such as hydroxyl oramino. The reactive groups will react with the silicon precursor to formSi—O—R or Si—NHR bonds (R represents an independently selected organicmoiety, e.g., an aryl or alkyl group, substituted or unsubstituted).These bonds will minimize the chance of phase separation between siliconmonomer and porogen during film deposition (spin coating); minimal phaseseparation will lead to the best possible film appearance and thicknessuniformity, and also minimize the pore size and distribution in thefinal film. Optionaly the porogen may have more than one reactive groupof the same or different function (e.g., one or more of —OH and/or(—NH₂, etc.). Simply by way of example, such groups are believed to forma covalent linkage between a porogen and the Si component of theresulting film in the form of Si—O—C or Si—N—C linkages.

[0078] Furthermore, the porogen should have a molecular weight andstructure such that it is readily and selectively removed from the filmwithout interfering with film formation. This is based on the nature ofsemiconductor devices, which typically have an upper limit to processingtemperatures. Broadly, a porogen should be removable from the newlyformed film at temperatures below, e.g., about 450° C. In particularembodiments, depending on the desired post film formation fabricationprocess and materials, the porogen is selected to be readily removed attemperatures ranging from about 300° C. to about 400° C. during a timeperiod ranging, e.g., from about 30 seconds to about 5 minutes. Forinstance, the very highest limit for multi-level interconnect processingin IC fabrication is 450° C., and many IC manufacturers require thehighest limit be 400° C. Further, in certain particular embodiments, theporogen is selected to be removed at a temperature of less than 300° C.The removal of the porogen may be induced by heating the film atatmospheric pressure or under a vacuum, or by exposing the film toradiation, or both.

[0079] Porogens which meet the above characteristics include thosecompounds and polymers which have a boiling point, sublimationtemperature, and/or decomposition temperature (at atmospheric pressure)range, for example, from about 175° C. to about 450° C., or in thisrange, to less than about 450° C. In particular embodiments, the boilingpoint, sublimation temperature, and/or decomposition temperature(s) ofthe porogen (at atmospheric pressure) are less than about 400° C., andin even more particular embodiments are less than about 300° C. Inaddition, poregens suitable for use according to the invention includethose having a molecular weight ranging, for example, from about 100 toabout 10,000 amu, and more preferably in the range of 100-3,000 amu.

[0080] Broadly, porogens suitable for use in the processes andcompositions of the invention include polymers, preferably those whichcontain one or more reactive groups, such as hydroxyl or amino.Advantageously, the molecular weights of selected polymers useful asporogens ranges, for example, from about 100 to about 10,000 amu. Inparticular embodiments, the molecular weight of the previously mentionedpolymers range, from about 100 to about 3,000 amu. Within these generalparameters, a suitable polymer porogen for use in the compositions andmethods of the invention is, e.g., a polyalkylene oxide, a monoether ofa polyalkylene oxide, an aliphatic polyester, an acrylic polymer, anacetal polymer, a poly(caprolatactone), a poly(valeractone), apoly(methyl methacrylate), a poly(vinylbutyral) and/or combinationsthereof. When the porogen is a polyalkylene oxide monoether, oneparticular embodiment is a C₁ to about C₆ alkyl, e.g., polyethyleneglycol monomethyl ether, or polypropylene glycol monomethyl ether.

[0081] Additional porogens suitable for use in the processes andcompositions of the invention include organic compounds. Specificcompounds useful as porogens include, for example: 1-adamantanol (CAS #768-95-6), 2-adamantanol (CAS # 700-57-2), 1-adamantanamine (CAS #768-94-5), 4-(1-adamantyl)phenol (CAS # 29799-07-03),4,4′-(1,3-adamantanediyl)diphenol (CAS # 37677-93-3), a-D-cellobioseoctaacetate (CAS # 5346-90-7), and cholesterol (CAS # 57-88-5).

[0082] Without meaning to be bound by any theory or hypothesis as to howthe invention might operate, it is believed that porogens that are,“readily removed from the film” undergo one or a combination of thefollowing events: (1) physical evaporation of the porogen during theheating step, (2)degradation of the porogen into more volatile molecularfragments, (3) breaking of the bond(s) between the porogen and the Sicontaining component, and subsequent evaporation of the porogen from thefilm, or any combination of modes 1-3. The porogen is heated until asubstantial proportion of the porogen is removed, e.g., at least about50% by weight, or more, of the porogen is removed. More particularly, incertain embodiments, depending upon the selected porogen and filmmaterials, at least about 75% by weight, or more, of the porogen isremoved. Thus, by “substantially” is meant, simply by way of example,removing from about 50% to about 75%, or more, of the original porogenfrom the applied film.

[0083] A porogen or porogens are present in the liquid precursorcomposition, for example, in a percentage ranging from about 1 to about40 weight percent, or more. More particularly, a porogent or porogensare present in the liquid precursor composition, e.g., in a percentageranging from about 2 to about 20 weight percent.

[0084] Solvents for Precursor Composition

[0085] The precursor composition optionally includes a solvent system.Reference herein to a “solvent” should be understood to encompass asingle solvent, polor or nonpolar and/or a combination of compatiblesolvents forming a solvent system selected to solubilize the precursormonomer or pre-polymer components, together with the other requiredcomponents of the precursor composition. A solvent is optionallyincluded in the precursor composition to lower its viscosity and promoteuniform coating onto a substrate by art-standard methods (e.g., spincoating, spray coating, dip coating, roller coating, and the like).

[0086] In order to facilitate solvent removal, the solvent is one whichhas a relatively low boiling point relative to the boiling point of anyselected porogen and the other precursor components. For example,solvents that are useful for the processes of the invention have aboiling point ranging from about 50 to about 175° C. For instance, whenthe solvent boiling point is 175° C., the boiling points and/orsublimation temperature of the porogen and silicon based monomer isgreater than 175° C., simply to allow the solvent to evaporate from theapplied film and leave the active portion of the precursor compositionin place. In order to meet various safety and environmentalrequirements, the solvent preferably has a high flash point (generallygreater than 40° C.) and relatively low levels of toxicity. A suitablesolvent includes, for example, hydrocarbons, as well as solvents havingthe functional groups C—O—C (ethers), —CO—O (esters), —CO— (ketones),—OH (alcohols), and —CO—N—(amides), and solvents which contain aplurality of these functional groups.

[0087] Simply by way of example, and without limitation, solvents forthe precursor composition include di-n-butyl ether, anisole, acetone,3-pentanone, 2-heptanone, ethyl acetate, n-propyl acetate, n-butylacetate, ethyl lactate, ethanol, 2-propanol, dimethyl acetamide,propylene glycol methyl ether acetate, and/or combinations thereof. Itis preferred that the solvent not react with the Si-based monomer orpolymer component of the precursor composition. Instead it is preferredthat only the porogen can react with the Si-based component. Therefore,the solvent should preferrably not contain hydroxyl or amino groups.

[0088] The solvent component is preferably present in an amount of fromabout 10% to about 90% by weight of the overall blend. A more preferredrange is from about 20% to about 75% and most preferably from about 20%to about 60%. The greater the percentage of solvent employed, thethinner is the resulting film. The greater the percentage of porogenemployed, the greater is the resulting porosity

[0089] Water as an Aging or Gelling Agent

[0090] As noted supra, in one embodiment of the invention thecomposition of the silicon-based precursor composition is selected toundergo aging or gelling in the presence of water, either liquid orwater vapor. Preferably, the precursor composition is applied to adesired substrate and then exposed to an ambient atmosphere thatincludes water vapor, e.g., at standard temperatures and standardatmospheric pressure. The higher the relative humidity of thesurrounding atmosphere, the faster the aging process will occur.Preferably, the approximately 40 percent relative humidity of theprocessing clean room is employed, so that no special additionalprocessing equipment or chambers are required. Of course, the relativehumidity can be varied as required for particular film formingconditions, to range, e.g., from a relative humidity of about 5% toabout 99%. Measured another way, for example, the desired exposure towater vapor is provided when the atmospheric partial pressure of watervapor ranges from, e.g., about 5 mm Hg to about 20 mm Hg,

[0091] As will be readily appreciated, the time period for exposure ofthe applied film to environmental water vapor is a time that issufficient for the film to attain sufficient condensation so thatremoval of the porgen is successfully accomplished. Simply by way ofexample, the time for exposure to environmental water vapor ranges froma minimum of about 5 to 10 seconds, up to 30 minutes or longer. Simplyby way of example, the applied precursor film is exposed toenvironmental water vapor for a time period ranging, e.g., from about 20seconds to about 5 mintues, or more particularly, for a time periodranging, e.g., from about 5 seconds to about 60 seconds.

[0092] Optionally, the precursor composition is prepared prior toapplication to a substrate to include water in a proportion suitable forinitiating aging of the precursor composition, without being present ina proportion that results in the precursor composition aging or gellingbefore it can be applied to a desired substrate. The water in theprecursor is optionally present in an amount sufficient to fully age thefilm without any need for further exposure to environmental water vapor,although any convenient combination of these sources of water to supportthe aging process is conveniently employed for particular desired filmforming situations.

[0093] Simply by way of example, the water is mixed into the precursorcomposition in a proportion ranging from

[0094] The mole ratio of water to the Si atoms in the monomer or polymercomponent is preferably from about 0 to about 50. A more preferred rangeis from about 0.1 to about 10 and most preferably from about 0.5 toabout 1.5. The acid may be present in a catalytic amount which can bereadily determined by those skilled in the art. Preferably the molarratio of acid to silane ranges from about 0 to about 10, more preferablyfrom about 0.001 to about 1.0, and most preferably from about 0.005 toabout 0.02.

[0095] Condensation Catalysts

[0096] The precursor composition preferrably contains an acid catalyst,such as glacial acetic acid; this catalyst will accelerate thehydrolysis and condensation reactions. Optionally, a base catalyst (suchas an alkali, ammonia or amine compounds with a pK_(b) ranging from lessthan 0 to about 9 can be added to the precursor composition for thispurpose. Amines, such as primary, secondary and tertiary alkyl amines,aryl amines, alcohol amines and mixtures thereof which have a boilingpoint of about 200° C. or less, preferably 100° C. or less and morepreferably 25° C. or less. Other amines, include, e.g., monoethanolamine, tetraethylenepentamine, 2-(aminoethylamino)ethanol,3-aminopropyltriethoxy silane, 3-amino-1,2-propanediol,3-(diethylamino)-1,2-propanediol,n-(2-aminoethyl)-3-aminopropyl-trimethoxy silane,3-aminopropyl-trimethoxy silane, methylamine, dimethylamine,trimethylamine, n-butylamine, n-propylamine, tetramethyl ammoniumhydroxide, piperidine and 2-methoxyethylamine.

[0097] It should also be mentioned, simply by way of example, that whenthe precursor comprises acetoxy silicon monomers, the water-inducedhydrolysis of the acetoxy compounds liberates acetic acid. The aceticacid catalyzes the further hydrolysis, and also accelerates condensationof the silicon precursor.

[0098] Optional Curing Steps

[0099] The artisan will appreciate that specific temperature ranges forcuring substrates comprising nanoporous dielectric films according tothe invention will depend upon the selected materials, substrate anddesired nanoscale pore structure, as is readily determined by routinemanipulation of these parameters. Generally, the curing step comprisesheating the previously prepared film at a temperature of at least 400°C. and for a time period ranging from about 10 to about 60 minutes, andis desirably conducted in the absence of oxygen, e.g., under an inertgas such as N₂, or in a vacuum. As exemplified herein, the films arecured at about 425° C. for about 30 minutes under vacuum.

[0100] The artisan will also appreciate that any number of additionalart-known curing methods are optionally employed, including theapplication of sufficient energy to cure the film by exposure of thefilm to electron beam energy, ultraviolet energy, microwave energy, andthe like, according to art-known methods.

EXAMPLES

[0101] The following non-limiting examples serve to illustrate theinvention.

Example 1 Nanoporous Silica Dielectric Film with 550 MW PEGMME with HeatAging

[0102] A precursor was prepared by combining, in a 100 ml roundbottomflask (containing a magnetic stirring bar), 10 g tetraacetoxysilane(United Chemical), 10 g methyltriacetoxysilane (United Chemical), and 30g acetone (Pacific Pac). These ingredients were combined within anN₂-environment (N₂ glove bag).

[0103] The flask was also connected to an N₂ environment to preventenvironmental moisture from entering the solution (standard temperatureand pressure).

[0104] After 20 minutes of stirring using the magnetic stirring bar, 1.5g of water was added to the flask. After 3 hours of continued stirringof the water-containing solution, 6.81 g of polyethylene glycolmonomethylether (“PEGMME” Aldrich; MW550 amu) was added as a porogen,and stirring continued for another 2 hrs. Thereafter, the resultingsolution was filtered through a 0.2 micron filter to provide theprecursor solution for the next step.

[0105] The precursor solution was then deposited onto a series of 4 inchsilicon wafers, each on a spin chuck and spun at 2500 rpm for 30seconds. The presence of water in the precursor resulted in the filmcoating being substantially condensed by the time that the wafer wasinserted into the first oven. Insertion into the first oven, asdiscussed below, took place within the 10 seconds of the completion ofspinning.

[0106] Each coated wafer was then transferred into a sequential seriesof ovens preset at specific temperatures, for one minute each. In thisexample, there were three ovens, and the preset oven temperatures were80° C., 175° C., and 300° C., respectively. The PEGMME was driven off bythese sequential heating steps as each wafer was moved through each ofthe three respective ovens.

[0107] Each wafer was cooled after receiving the three-oven stepped heattreatment, and the produced dielectric film was measured usingellipsometry to determine its thickness and refractive index. Eachfilm-coated wafer was then further cured at 425° C. for 30 minutes undervacuum.

[0108] Results

[0109] A film is judged to be porous if its refractive index (n) is lessthan 1.44. A non-porous film made from the liquid precursor of thisinvention will have a refractive index of 1.44. In comparison, air has arefractive index of 1.0. The porosity of a nanoporous film of theinvention, is therefore proportional to the percentage of its volumethat is air. The porosity of a film is inversely proportional to n-1.For example, a film with n=1.27 will have porosity of:100*[(1.44-1)−(1.27-1)]/(1.44-1)=39%.

[0110] The measurements obtained from a representative nanoporous silicadielectric film produced by the methods of this example on a wafer, areshown in Table 1, below. TABLE 1 Bake Thickness (Å) Bake RI# CureThickness (Å) Cure RI 6622 1.255 5902 1.250

[0111] Application of the above-equation indicates that the cured filmproduced by the above-described method has a porosity of about 43%.

Example 2 Nanoporous Silica Dielectric Film with 550 MW PEGMME with H₂OAging

[0112] A precursor was prepared as described for Example 1, supra. Theprepared precursor mixture was deposited onto a series of 4 inch siliconwafers, which were each mounted on a spin chuck. Each coated wafer wasspun at 2500 rpm for 30 seconds, and the presence of water in theprecursor resulted in the film coating being substantially condensed bythe time that the wafer was inserted into the oven. Insertion into theoven, as discussed below, took place within the 10 seconds of thecompletion of spinning.

[0113] The coated wafers were each then heated for 1 or 3 minutes in asingle oven, at one of the following alternative temperatures: 200° C.,225° C., 250° C., 270° C., or 300° C., to determine the optimumtemperature range for porogen removal.

[0114] Each heated wafer was then cooled, and the resulting film on eachwafer was measured using ellipsometry to determine its thickness andrefractive index (which can be correlated to the film's porosity.) Eachfilm was then cured at 425° C. for 30 minutes under vacuum.

[0115] Results

[0116] Measurements of film thickness and refractive index fornanoporous silica dielectric films produced and heated as describedabove are summarized in Table 2, below. TABLE 2 Bake Bake Bake TimeThickness Cure Thickness Temp. (min) (Å) Bake RI# (Å) Cure RI# 200° C. 19392 1.443 6619 1.251 3 8047 1.375 N/A* cracked 225° C. 1 9127 1.4406537 1.258 3 7442 1.348 N/A* cracked 250° C. 1 7801 1.291 N/A* cracked 37613 1.286 N/A* cracked 270° C. 1 7704 1.254 6730 1.247 3 7588 1.2526380 1.261 300° C. 1 7697 1.240 6405 1.258 3 7550 1.238 6499 1.258

[0117] As can be appreciated from an inspection of the above results,the best results were obtained with a brief 1 or 3 minute oven treatmentat 270° C. or greater, which both drove off the porogen andsubstantially cured the film. Heating at 300° C. certainly drove offmost or all of the porogen. The films after a final cure step show aslightly decreased film thickness and a slightly greater RI, confirmingthat curing does further increased the film density. However, thechanges are relatively minor, and it is expected that the cure step willbe rendered unnecessary by a modest increase in the duration andtemperature of the porogen removal step.

[0118] In addition, the film made using bake temperature of 270° C. andbake time of 1 minute (See Table 2, supra) was confirmed by measurementsto have an average pore size of about 20 Å (2 nanometers). In contrast,films obtained by previously employed methods have average porediameters of, e.g., 60 Å (6 nanometers). Further, the film produced bythe instant example had virtually no pores larger than 100 Å (10nanometers). The pore size distribution was obtained by the art-knownmethod of isothermal nitrogen adsorption which is based upon theBrunauer Emmett Teller (BET) and Kelvin theories (see, e.g., Ralph K.Iler, 1979, Chemistry of Silica, John Wiley and Sons, PP467 and 488-502,the disclosure of which is incorporated by reference herein). Thismeasurement data confirms that films having nanometer scale porestructure can be produced by the method of this invention.

Example 3 Nanoporous Silica Dielectric Film with 550 MW PPGMBE with HeatAging

[0119] A precursor was prepared as described for Example 1,supra, but adifferent porogen, polypropylene glycol monobutyl ether (PPGMBE; mw 340amu), was employed. The prepared precursor was then deposited onto 4inch silicon wafers, each on a spin chuck. Each wafer was spun at 2500rpm for 30 seconds. The presence of water in the precursor resulted inthe film coating being substantially condensed by the time that thewafer was inserted into the oven. Insertion into first oven, asdiscussed below, took place within the 10 seconds of the completion ofspinning.

[0120] As for Example 1, supra, each coated wafer was then transferredinto a sequential series of ovens preset at specific temperatures, forone minute each as preset temperatures of 80° C., 175° C., and 300° C.,respectively. Each wafer was cooled after receiving the three-ovenstepped heat treatment, and the produced dielectric film measured usingellipsometry to determine its thickness and refractive index. Eachfilm-coated wafer was then further cured at 425° C. for 30 minutes undervacuum. Bake Thickness (Å) Bake RI Cure Thickness (Å) Cure RI 8168 1.2777064 1.251

[0121] The above results confirm that films can be made with a secondporogen.

Example 4 Nanoporous Silica Dielectric Film with 340 MW PPGMBE with H₂OAging

[0122] Precursor was made as described above for Example 3,supra. Theresulting films were measured and the data summarized in the followingtable. Bake Bake Cure Bake Time Thickness Thickness Temp. (min) (Å) BakeRI (Å) Cure RI 200° C. 1 6312 1.374 4881 1.269 3 6187 1.374 4676 1.272250° C. 1 6593 1.322 4911 1.279 3 5844 1.306 4847 1.273 270° C. 1 62531.279 4982 1.283 3 6042 1.285 5099 1.285 300° C. 1 6557 1.270 5076 1.2783 6199 1.269 5228 1.279

Example 5 Control Experiment—Water Added

[0123] Precursor was made as described for Example 1, supra. The mixturewas deposited onto a 4 inch silicon wafer on a spin chuck. It was spunat 2500 rpm for 30 seconds. The film was heated for 1 minute in ovens at80° C., 175° C., and 300° C. The wafer was then cooled and the filmmeasured using ellipsometry to determine its thickness and refractiveindex (which can be correlated to the film's porosity.) The film wasthen cured at 425° C. for 30 minutes under nitrogen.

[0124] The cohesive strength was measured by the “stud pull method”which is described, for example, in co-owned U.S. Ser. No. 09/111,084,filed Jul. 7, 1998, incorporated by reference herein in its entirety.Cure Cohesive Strength Thickness (Å) Cure RI k¹ (kpsi) 4572 1.2468 2.37.5

Example 6 No Water Added

[0125] Precursor was made by mixing 10 g tetraactoxysilane (UnitedChemical), 10 g methyltriacetoxysilane (United Chemical), 30 g acetone(Pacific Pac), and 1.5 ml of dried glacial acetic acid (Aldrich) in adry bag. After 3 hours of mixing, 6.81 g of 550 MW polyethyleneglycolmonomethylether (Aldrich) was added as a porogen. This was then mixedfor 2 hrs and then filtered with 0.2 micron filter.

[0126] The processing facility is one in which the relative humidity ofthe air is maintained at about 40% relative humidity.

[0127] The mixture was deposited onto a 4 inch silicon wafer on a spinchuck. It was spun at 2500 rpm for 30 seconds. Sufficient moisture wasabsorbed into the applied precursor during processing to substantiallyage or condense the applied film. The time between the end of spinningand oven insertion was, as described previously, about 10 seconds.

[0128] The film was heated for 1 minute in ovens @ 80° C., 175° C., and300° C. The wafer was then cooled and the film was measured usingellipsometry to determine its thickness and refractive index (which canbe correlated to the films porosity.) The film was then cured at 425° C.for 30 minutes with nitrogen. Cure Cohesive Strength Thickness (Å) CureRI k (kpsi) 5240 1.215 1.99 5.5

[0129] The above results confirm that water induced aging orcondensation was achieved simply by absorption of water vapor fromenvironmental air, in an environmentally controlled processing facility.

DISCUSSION

[0130] Comparative examples 5 and 6, described supra, confirm that thewater-aged film has substantial cohesive strength relative to film agedwithout water. The cohesive strength measurement obtained above, e.g.,Example 5, confirm that the nanoporous dielectric silica films producedby the methods of the present invention are substantially stronger thanthose obtained by application of previous methods, while retainingsimilar dielectric, constant values.

What is claimed is:
 1. A method of producing a nanoporous silicadielectric film by a process comprising (a) preparing a silicon-based,precursor composition comprising a porogen, (b) coating a substrate withthe silicon-based precursor to form a film, (c) aging or condensing thefilm in the presence of water, (d) heating the gelled film at atemperature and for a duration effective to remove substantially all ofsaid porogen, and wherein said precursor composition is substantiallyaged or condensed in the presence of water in liquid or vapor form,without the application of heat or exposure to external catalyst.
 2. Themethod of claim 1 wherein the silicon-based precursor compositioncomprises water in a molar ratio of water to Si ranging from about 2:1to about 0:1.
 3. The method of claim 1 wherein the silicon-basedprecursor composition comprises a monomer or prepolymer of Formula I:Rx—Si—Ly  (Formula I) wherein x is an integer ranging from 0 to about 2,and y is an integer ranging from about 2 to about 4; R is independentlyselected from the group consisting of alkyl, aryl, hydrogen andcombinations thereof; L is an electronegative moiety, independentlyselected from the group consisting of alkoxy, carboxy, amino, amido,halide, isocyanato and combinations thereof.
 4. The method of claim 3wherein the silicon-based precursor composition further comprises apolymer formed by condensing a monomer or prepolymer according toFormula I, wherein the number average molecular weight of said polymerranges from about 150 to about 10,000 amu.
 5. The method of claim 3wherein the silicon-based precursor composition comprises a monomer orprecursor that is selected from the group consisting of anacetoxysilane, an ethoxysilane, a methoxysilane, and combinationsthereof.
 6. The method of claim 5 wherein the silicon-based precursorcomposition comprises a monomer or precursor that is selected from thegroup consisting of tetraacetoxysilane, a C₁ to about C₆ alkyl oraryl-triacetoxysilane, and combinations thereof.
 7. The method of claim6 wherein said triacetoxysilane is methyltriacetoxysilane.
 8. The methodof claim 3 wherein the silicon-based precursor composition comprises amonomer or precursor that is selected from the group consisting oftetrakis(2,2,2-trifluoroethoxy)silane, tetrakis(trifluoroacetoxy)silane,tetraisocyanatosilane, tris(2,2,2-trifluoroethoxy)methylsilane,tris(trifluoroacetoxy)methylsilane, methyltriisocyanatosilane andcombinations thereof.
 9. The method of claim 1 wherein at least aportion of the water of step (c) is absorbed from atmospheric watervapor.
 10. The method of claim 1 wherein all of the water of step (c) isabsorbed from atmospheric water vapor.
 11. The method of claim 9 whereinthe atmospheric partial pressure of water vapor ranges from about 5 mmHg to about 20 mm Hg,
 12. The method of claim 9 wherein the film isexposed to atmospheric water vapor for a time period effective for agingthe applied film.
 13. The method of claim 12 wherein the film is exposedto atmospheric water vapor for a time period ranging from about 20seconds to about 5 minutes.
 14. The process of claim 1 furthercomprising a curing step conducted at a temperature and for a durationsufficient to render the thickness and density of the produced filmstable for use in a semiconductor device.
 15. The process of claim 1wherein the porogen has a boiling point, sublimation point ordecomposition temperature ranging from about 175° C. to about 450° C.16. The process of claim 1 wherein heating step (d) comprises heatingthe film at a temperature ranging from about 175° C. to about 300° C.,for a time period ranging from about 30 seconds to about 5 minutes, toremove substantially all porogen.
 17. The process of claim 1 wherein theporogen is selected to covalently bond to a silicon component of theprecursor composition, and remains covalently bonded thereto, until theheating of step (d).
 18. The process of claim 1 wherein the porogen hasa molecular weight ranging from about 100 to about 10,000 amu,
 19. Theprocess of claim 18 wherein the porogen has a molecular weight rangingfrom about 100 to about 3,000 amu,
 20. The process of claim 1 whereinthe porogen comprises a reagent comprising at least one reactivehydroxyl or amino functional group, and said reagent is selected fromthe group consisting of an organic compound, an organic polymer, aninorganic polymer and combinations thereof.
 21. The process of claim 1wherein the porogen is a compound selected from the group consisting of1-adamantanol, 2-adamantanol, 1-adamantanamine, 4-(1-adamantyl)phenol,4,4-(1,3-adamantanediyl)diphenol, a-D-cellobiose octaacetate, andcholesterol.
 22. The process of claim 1 wherein the porogen is selectedfrom the group consisting of a polyalkylene oxide, a monoether of apolyalkylene oxide, an aliphatic polyester, an acrylic polymer, anacetal polymer, a poly(caprolatactone), a poly(valeractone), apoly(methyl methacrylate), a poly (vinylbutyral) and combinationsthereof.
 23. The process of claim 22 wherein the polyalkylene oxidemonoether comprises a C₁ to about C₆ alkyl chain between oxygen atomsand a C1 to about C6 alkyl ether moiety, and wherein the alkyl chain issubstituted or unsubstituted.
 24. The process of claim 23 wherein thepolyalkylene oxide monoether is a polyethylene glycol monomethyl etheror polypropylene glycol monobutyl ether.
 25. The process of claim 1wherein the porogen is present in the composition in a ratio rangingfrom about 2 to about 20 weight percent.
 26. The process of claim 1wherein the silicon-based, precursor composition further comprises asolvent.
 27. The process of claim 26 wherein the silicon-based,precursor composition comprises solvent in an amount ranging from about10% to about 90% by weight.
 28. The process of claim 26 wherein thesolvent has a boiling point ranging from about 50 to about 175° C. 29.The process of claim 26 wherein the solvent is selected from the groupconsisting of hydrocarbons, esters, ethers, ketones, alcohols, amidesand combinations thereof.
 30. The process of claim 26 wherein thesolvent is not an alcohol when the silicon based monomer or precursorcomprises an acetoxy-functional group.
 31. The process of claim 26wherein the solvent does not comprise hydroxyl or amino groups.
 32. Theprocess of claim 26 wherein the solvent is selected from the groupconsisting of di-n-butyl ether, anisole, acetone, 3-pentanone,2-heptanone, ethyl acetate, n-propyl acetate, n-butyl acetate,2-propanol, dimethyl acetamide, propylene glycol methyl ether acetate,and/or combinations thereof.
 33. A nanoporous dielectric film producedon a substrate by the process of claim
 1. 34. A semiconductor devicecomprising a nanoporous dielectric film of claim
 33. 35. Thesemiconductor device of claim 34 that is an integrated circuit.